Icompatible change in V01.18 to V01.16 under system typeplate REST API

Hello,

in the GET "typeplate" call to the System REST API, the response body between V01.16 and V01.18 has changed.

Response body in V01.16:

{
"typePlateType": "ctrlXCORE",
"serialNumber": "xxxxxxxxxxx",
"materialIndex": "AB1",
"materialNumber": "R9114xxxx",
"typeCode": "COREX-C-X3-11-ANNN-21.01-01RS-NN-NN"
}

Response body in V01.18:

{
"typePlateType": "ctrlXCORE",
"serialNumber": "xxxxxxxxxxx",
"materialIndex": "AB1",
"typeCode": "COREX-C-X3-11-ANNN-21.01-01RS-NN-NN",
"hardwareRevision": "cx_m4_a"
}

REST API URL used on both images: /system/api/v1/typeplate

Is this change intended or an bug?
If the change is permanent, where is the materialNumber available via the REST API?

Thanks